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<h1>6 IDL to C mapping</h1>
<h3><a name="id69337">6.1
Introduction</a></h3>
<p>The IC C mapping (used by the C client and C server back-ends) follows
the <strong>OMG C Language Mapping Specification</strong>. </p>
<p>The C mapping supports the following:</p>
<ul>
<li>
<p>All OMG IDL basic types except <span class="code">long double</span> and <span class="code">any</span>.</p>
</li>
<li>
<p>All OMG IDL constructed types.</p>
</li>
<li>
<p>OMG IDL constants.</p>
</li>
<li>
<p>Operations with passing of parameters and receiving of
results. <span class="code">inout</span> parameters are not supported.</p>
</li>
</ul>
<p>The following is not supported:
</p>
<ul>
<li>
<p>Access to attributes.</p>
</li>
<li>
<p>User defined exceptions.</p>
<p></p>
</li>
<li>
<p>User defined objects.</p>
<p></p>
</li>
</ul>
<h3><a name="id69440">6.2
C Mapping Characteristics</a></h3>
<h4>Reserved Names</h4>
<p>The IDL compiler reserves all identifiers starting with
<span class="code">OE_</span> and <span class="code">oe_</span> for internal use.</p>
<h4>Scoped Names</h4>
<p>The C programmer must always use the global name for a type,
constant or operation. The C global name corresponding to an
OMG IDL global name is derived by converting occurrences of
"::" to underscore, and eliminating the leading "::". So, for
example, an operation <span class="code">op1</span> defined in interface
<span class="code">I1</span> which is defined in module <span class="code">M1</span> would be
written as <span class="code">M1::I1::op1</span> in IDL and as <span class="code">M1_I1_op1</span>
in C.</p>
<div class="warning">
<div class="label">Warning</div>
<div class="content"><p>
<p>If underscores are used in IDL names it can lead to
ambiguities due to the name mapping described above,
therefore it is advisable to avoid underscores in
identifiers.</p>
</p></div>
</div>
<h4>Generated Files</h4>
<p>Two files will be generated for each scope. One set of files
will be generated for each module and each interface scope.
An extra set is generated for those definitions at top
level scope. One of the files is a header file(<span class="code">.h</span>), and the
other file is a C source code file (<span class="code">.c</span>). In addition to these
files a number of C source files will be generated for type encodings,
they are named according to the following template:
<span class="code">oe_code_<type>.c</span>.</p>
<p>For example:</p>
<div class="example"><pre>
// IDL, in the file "spec.idl"
module m1 {
typedef sequence<long> lseq;
interface i1 {
...
};
...
};
</pre></div>
<p>XXX This is C client specific.
Will produce the files <span class="code">oe_spec.h</span> and
<span class="code">oe_spec.c</span> for the top scope level. Then the files
<span class="code">m1.h</span> and <span class="code">m1.c</span> for the module <span class="code">m1</span> and
files <span class="code">m1_i1.h</span> and <span class="code">m1_i1.c</span> for the interface
<span class="code">i1</span>. The typedef will produce <span class="code">oe_code_m1_lseq.c</span>.</p>
<p>The header file contains type definitions for all
<span class="code">struct</span> types and sequences and constants in the IDL file. The
c file contains all operation stubs if the the scope is an interface.</p>
<p>In addition to the scope-related files a C source file will
be generated for encoding operations of all <span class="code">struct</span> and
sequence types.</p>
<h3><a name="id69638">6.3
Basic OMG IDL Types</a></h3>
<p>The mapping of basic types is as follows.</p>
<table border="1" cellpadding="2" cellspacing="0">
<tr>
<td align="left" valign="middle"><strong>OMG IDL type</strong></td>
<td align="left" valign="middle"><strong>C type</strong></td>
<td align="left" valign="middle"><strong>Mapped to C type</strong></td>
</tr>
<tr>
<td align="left" valign="middle">float</td>
<td align="left" valign="middle">CORBA_float</td>
<td align="left" valign="middle">float</td>
</tr>
<tr>
<td align="left" valign="middle">double</td>
<td align="left" valign="middle">CORBA_double</td>
<td align="left" valign="middle">double</td>
</tr>
<tr>
<td align="left" valign="middle">short</td>
<td align="left" valign="middle">CORBA_short</td>
<td align="left" valign="middle">short</td>
</tr>
<tr>
<td align="left" valign="middle">unsigned short</td>
<td align="left" valign="middle">CORBA_unsigned_short</td>
<td align="left" valign="middle">unsigned short</td>
</tr>
<tr>
<td align="left" valign="middle">long</td>
<td align="left" valign="middle">CORBA_long</td>
<td align="left" valign="middle">long</td>
</tr>
<tr>
<td align="left" valign="middle">long long</td>
<td align="left" valign="middle">CORBA_long_long</td>
<td align="left" valign="middle">long</td>
</tr>
<tr>
<td align="left" valign="middle">unsigned long</td>
<td align="left" valign="middle">CORBA_unsigned_long</td>
<td align="left" valign="middle">unsigned long</td>
</tr>
<tr>
<td align="left" valign="middle">unsigned long long</td>
<td align="left" valign="middle">CORBA_unsigned_long_long</td>
<td align="left" valign="middle">unsigned long</td>
</tr>
<tr>
<td align="left" valign="middle">char</td>
<td align="left" valign="middle">CORBA_char</td>
<td align="left" valign="middle">char</td>
</tr>
<tr>
<td align="left" valign="middle">wchar</td>
<td align="left" valign="middle">CORBA_wchar</td>
<td align="left" valign="middle">unsigned long</td>
</tr>
<tr>
<td align="left" valign="middle">boolean</td>
<td align="left" valign="middle">CORBA_boolean</td>
<td align="left" valign="middle">unsigned char</td>
</tr>
<tr>
<td align="left" valign="middle">octet</td>
<td align="left" valign="middle">CORBA_octet</td>
<td align="left" valign="middle">char</td>
</tr>
<tr>
<td align="left" valign="middle">any</td>
<td align="left" valign="middle">Not supported</td>
<td align="left" valign="middle"></td>
</tr>
<tr>
<td align="left" valign="middle">long double</td>
<td align="left" valign="middle">Not supported</td>
<td align="left" valign="middle"></td>
</tr>
<tr>
<td align="left" valign="middle">Object</td>
<td align="left" valign="middle">Not supported</td>
<td align="left" valign="middle"></td>
</tr>
<tr>
<td align="left" valign="middle">void</td>
<td align="left" valign="middle">void</td>
<td align="left" valign="middle">void</td>
</tr>
</table>
<em>Table
6.1:
OMG IDL Basic Types</em>
<p>XXX Note that several mappings are not according to OMG C Language
mapping.</p>
<h3><a name="id70147">6.4
Constructed OMG IDL Types</a></h3>
<p>Constructed types have mappings as shown in the following table.</p>
<table border="1" cellpadding="2" cellspacing="0">
<tr>
<td align="left" valign="middle">OMG IDL type</td>
<td align="left" valign="middle">Mapped to C type</td>
</tr>
<tr>
<td align="left" valign="middle">string</td>
<td align="left" valign="middle">CORBA_char*</td>
</tr>
<tr>
<td align="left" valign="middle">wstring</td>
<td align="left" valign="middle">CORBA_wchar*</td>
</tr>
<tr>
<td align="left" valign="middle">struct</td>
<td align="left" valign="middle">struct</td>
</tr>
<tr>
<td align="left" valign="middle">union</td>
<td align="left" valign="middle">union</td>
</tr>
<tr>
<td align="left" valign="middle">enum</td>
<td align="left" valign="middle">enum</td>
</tr>
<tr>
<td align="left" valign="middle">sequence</td>
<td align="left" valign="middle">struct (see below)</td>
</tr>
<tr>
<td align="left" valign="middle">array</td>
<td align="left" valign="middle">array</td>
</tr>
</table>
<em>Table
6.2:
OMG IDL Constructed Types</em>
<p>An OMG IDL sequence (an array of variable length), </p>
<div class="example"><pre>
// IDL
typedef sequence <IDL_TYPE> NAME;
</pre></div>
<p>is mapped to a C struct as follows:</p>
<div class="example"><pre>
/* C */
typedef struct {
CORBA_unsigned_long _maximum;
CORBA_unsigned_long _length;
C_TYPE* _buffer;
} C_NAME;
</pre></div>
<p>where <span class="code">C_TYPE</span> is the mapping of <span class="code">IDL_TYPE</span>, and where
<span class="code">C_NAME</span> is the scoped name of <span class="code">NAME</span>.</p>
<h3><a name="id71595">6.5
OMG IDL Constants</a></h3>
<p>An IDL constant is mapped to a C constant through a C
<span class="code">#define</span> macro, where the name of the macro is scoped.
Example:</p>
<div class="example"><pre>
// IDL
module M1 {
const long c1 = 99;
};
</pre></div>
<p>results in the following:</p>
<div class="example"><pre>
/* C */
#define M1_c1 99
</pre></div>
<h3><a name="id71622">6.6
OMG IDL Operations</a></h3>
<p>An OMG IDL operation is mapped to C function. Each C operation
function has two mandatory parameters: a first parameter of
<strong>interface object</strong> type, and a last parameter of
<strong>environment</strong> type.</p>
<p></p>
<p>In a C operation function the the <span class="code">in</span> and <span class="code">out</span>
parameters are located between the first and last parameters
described above, and they appear in the same order as in the IDL
operation declaration.</p>
<p>Notice that <span class="code">inout</span> parameters are not supported. </p>
<p></p>
<p>The return value of an OMG IDL operation is mapped to a
corresponding return value of the C operation function.</p>
<p>Mandatory C operation function parameters:</p>
<ul>
<li>
<span class="code">CORBA_Object oe_obj</span> - the first parameter of a C
operation function. This parameter is required by the <strong>OMG C Language Mapping Specification</strong>, but in the current
implementation there is no particular use for it.</li>
<li>
<p><span class="code">CORBA_Environment* oe_env</span> - the last parameter of a C
operation function. The parameter is defined in the C header
file <span class="code">ic.h</span> and has the following public fields:</p>
<ul>
<li>
<p><span class="code">CORBA_Exception_type _major</span> - indicates if an
operation invocation was successful which will be one of
the following:</p>
<ul>
<li>CORBA_NO_EXCEPTION</li>
<li>CORBA_SYSTEM_EXCEPTION</li>
</ul>
</li>
<li>int <strong>_fd</strong> - a file descriptor returned from
<strong>erl_connect</strong> function.</li>
<li>int <strong>_inbufsz</strong> - size of input buffer.</li>
<li>char* <strong>_inbuf</strong> - pointer to a buffer used for
input.</li>
<li>int <strong>_outbufsz</strong> - size of output buffer.</li>
<li>char* <strong>_outbuf</strong> - pointer to a buffer used for
output.</li>
<li>
<p>int <strong>_memchunk</strong> - expansion unit size for the
output buffer. This is the size of memory chunks in
bytes used for increasing the output in case of buffer
expansion. The value of this field must be always set
to >= 32, should be at least 1024 for performance
reasons.</p>
</li>
<li>char <strong>regname[256]</strong> - a registered name for a
process.</li>
<li>erlang_pid* <strong>_to_pid</strong> - an Erlang process
identifier, is only used if the registered_name parameter
is the empty string.</li>
<li>erlang_pid* <strong>_from_pid</strong> - your own process id so
the answer can be returned</li>
</ul>
<p>Beside the public fields, other private fields
are internally used but are not mentioned here. </p>
</li>
</ul>
<p>Example:</p>
<div class="example"><pre>
// IDL
interface i1 {
long op1(in long a);
long op2(in string s, out long count);
};
</pre></div>
<p>Is mapped to the following C functions</p>
<div class="example"><pre>
/* C */
CORBA_long i1_op1(i1 oe_obj, CORBA_long a, CORBA_Environment* oe_env)
{
...
}
CORBA_long i1_op2(i1 oe_obj, CORBA_char* s, CORBA_long *count,
CORBA_Environment* oe_env)
{
...
}
</pre></div>
<a name="op_impl"></a>
<h4>Operation Implementation</h4>
<p>There is no standard CORBA mapping for the C-server side,
as it is implementation-dependent but built in a similar way.
The current server side mapping is different from the client
side mapping in several ways:</p>
<ul>
<li>Argument mappings</li>
<li>Result values</li>
<li>Structure</li>
<li>Usage</li>
<li>Exception handling</li>
</ul>
<h3><a name="id71884">6.7
Exceptions</a></h3>
<p>Although exception mapping is not implemented, the stubs will
generate CORBA system exceptions in case of operation failure.
Thus, the only exceptions propagated by the system are built in
system exceptions.</p>
<h3><a name="id71897">6.8
Access to Attributes</a></h3>
<p>Not Supported</p>
<h3><a name="id71908">6.9
Summary of Argument/Result Passing for the C-client</a></h3>
<p>The user-defined parameters can only be <span class="code">in</span> or <span class="code">out</span>
parameters, as
<span class="code">inout</span> parameters are not supported.</p>
<p>This table summarize the types a client passes as arguments to
a stub, and receives as a result.</p>
<table border="1" cellpadding="2" cellspacing="0">
<tr>
<td align="left" valign="middle">OMG IDL type</td>
<td align="left" valign="middle">In</td>
<td align="left" valign="middle">Out</td>
<td align="left" valign="middle">Return</td>
</tr>
<tr>
<td align="left" valign="middle">short</td>
<td align="left" valign="middle">CORBA_short</td>
<td align="left" valign="middle">CORBA_short*</td>
<td align="left" valign="middle">CORBA_short</td>
</tr>
<tr>
<td align="left" valign="middle">long</td>
<td align="left" valign="middle">CORBA_long</td>
<td align="left" valign="middle">CORBA_long*</td>
<td align="left" valign="middle">CORBA_long</td>
</tr>
<tr>
<td align="left" valign="middle">long long</td>
<td align="left" valign="middle">CORBA_long_long</td>
<td align="left" valign="middle">CORBA_long_long*</td>
<td align="left" valign="middle">CORBA_long_long</td>
</tr>
<tr>
<td align="left" valign="middle">unsigned short</td>
<td align="left" valign="middle">CORBA_unsigned_short</td>
<td align="left" valign="middle">CORBA_unsigned_short*</td>
<td align="left" valign="middle">CORBA_unsigned_short</td>
</tr>
<tr>
<td align="left" valign="middle">unsigned long</td>
<td align="left" valign="middle">CORBA_unsigned_long</td>
<td align="left" valign="middle">CORBA_unsigned_long*</td>
<td align="left" valign="middle">CORBA_unsigned_long</td>
</tr>
<tr>
<td align="left" valign="middle">unsigned long long</td>
<td align="left" valign="middle">CORBA_unsigned_long_long</td>
<td align="left" valign="middle">CORBA_unsigned_long_long*</td>
<td align="left" valign="middle">CORBA_unsigned_long_long</td>
</tr>
<tr>
<td align="left" valign="middle">float</td>
<td align="left" valign="middle">CORBA_float</td>
<td align="left" valign="middle">CORBA_float*</td>
<td align="left" valign="middle">CORBA_float</td>
</tr>
<tr>
<td align="left" valign="middle">double</td>
<td align="left" valign="middle">CORBA_double</td>
<td align="left" valign="middle">CORBA_double*</td>
<td align="left" valign="middle">CORBA_double</td>
</tr>
<tr>
<td align="left" valign="middle">boolean</td>
<td align="left" valign="middle">CORBA_boolean</td>
<td align="left" valign="middle">CORBA_boolean*</td>
<td align="left" valign="middle">CORBA_boolean</td>
</tr>
<tr>
<td align="left" valign="middle">char</td>
<td align="left" valign="middle">CORBA_char</td>
<td align="left" valign="middle">CORBA_char*</td>
<td align="left" valign="middle">CORBA_char</td>
</tr>
<tr>
<td align="left" valign="middle">wchar</td>
<td align="left" valign="middle">CORBA_wchar</td>
<td align="left" valign="middle">CORBA_wchar*</td>
<td align="left" valign="middle">CORBA_wchar</td>
</tr>
<tr>
<td align="left" valign="middle">octet</td>
<td align="left" valign="middle">CORBA_octet</td>
<td align="left" valign="middle">CORBA_octet*</td>
<td align="left" valign="middle">CORBA_octet</td>
</tr>
<tr>
<td align="left" valign="middle">enum</td>
<td align="left" valign="middle">CORBA_enum</td>
<td align="left" valign="middle">CORBA_enum*</td>
<td align="left" valign="middle">CORBA_enum</td>
</tr>
<tr>
<td align="left" valign="middle">struct, fixed</td>
<td align="left" valign="middle">struct*</td>
<td align="left" valign="middle">struct*</td>
<td align="left" valign="middle">struct</td>
</tr>
<tr>
<td align="left" valign="middle">struct, variable</td>
<td align="left" valign="middle">struct*</td>
<td align="left" valign="middle">struct**</td>
<td align="left" valign="middle">struct*</td>
</tr>
<tr>
<td align="left" valign="middle">union, fixed</td>
<td align="left" valign="middle">union*</td>
<td align="left" valign="middle">union*</td>
<td align="left" valign="middle">union</td>
</tr>
<tr>
<td align="left" valign="middle">union, variable</td>
<td align="left" valign="middle">union*</td>
<td align="left" valign="middle">union**</td>
<td align="left" valign="middle">union*</td>
</tr>
<tr>
<td align="left" valign="middle">string</td>
<td align="left" valign="middle">CORBA_char*</td>
<td align="left" valign="middle">CORBA_char**</td>
<td align="left" valign="middle">CORBA_char*</td>
</tr>
<tr>
<td align="left" valign="middle">wstring</td>
<td align="left" valign="middle">CORBA_wchar*</td>
<td align="left" valign="middle">CORBA_wchar**</td>
<td align="left" valign="middle">CORBA_wchar*</td>
</tr>
<tr>
<td align="left" valign="middle">sequence</td>
<td align="left" valign="middle">sequence*</td>
<td align="left" valign="middle">sequence**</td>
<td align="left" valign="middle">sequence*</td>
</tr>
<tr>
<td align="left" valign="middle">array, fixed</td>
<td align="left" valign="middle">array</td>
<td align="left" valign="middle">array</td>
<td align="left" valign="middle">array_slice*</td>
</tr>
<tr>
<td align="left" valign="middle">array, variable</td>
<td align="left" valign="middle">array</td>
<td align="left" valign="middle">array_slice**</td>
<td align="left" valign="middle">array_slice*</td>
</tr>
</table>
<em>Table
6.3:
Basic Argument and Result passing</em>
<p>A client is responsible for providing storage of all arguments passed
as <strong>in</strong> arguments.</p>
<table border="1" cellpadding="2" cellspacing="0">
<tr>
<td align="left" valign="middle">OMG IDL type</td>
<td align="left" valign="middle">Out</td>
<td align="left" valign="middle">Return</td>
</tr>
<tr>
<td align="left" valign="middle">short</td>
<td align="left" valign="middle">1</td>
<td align="left" valign="middle">1</td>
</tr>
<tr>
<td align="left" valign="middle">long</td>
<td align="left" valign="middle">1</td>
<td align="left" valign="middle">1</td>
</tr>
<tr>
<td align="left" valign="middle">long long</td>
<td align="left" valign="middle">1</td>
<td align="left" valign="middle">1</td>
</tr>
<tr>
<td align="left" valign="middle">unsigned short</td>
<td align="left" valign="middle">1</td>
<td align="left" valign="middle">1</td>
</tr>
<tr>
<td align="left" valign="middle">unsigned long</td>
<td align="left" valign="middle">1</td>
<td align="left" valign="middle">1</td>
</tr>
<tr>
<td align="left" valign="middle">unsigned long long</td>
<td align="left" valign="middle">1</td>
<td align="left" valign="middle">1</td>
</tr>
<tr>
<td align="left" valign="middle">float</td>
<td align="left" valign="middle">1</td>
<td align="left" valign="middle">1</td>
</tr>
<tr>
<td align="left" valign="middle">double</td>
<td align="left" valign="middle">1</td>
<td align="left" valign="middle">1</td>
</tr>
<tr>
<td align="left" valign="middle">boolean</td>
<td align="left" valign="middle">1</td>
<td align="left" valign="middle">1</td>
</tr>
<tr>
<td align="left" valign="middle">char</td>
<td align="left" valign="middle">1</td>
<td align="left" valign="middle">1</td>
</tr>
<tr>
<td align="left" valign="middle">wchar</td>
<td align="left" valign="middle">1</td>
<td align="left" valign="middle">1</td>
</tr>
<tr>
<td align="left" valign="middle">octet</td>
<td align="left" valign="middle">1</td>
<td align="left" valign="middle">1</td>
</tr>
<tr>
<td align="left" valign="middle">enum</td>
<td align="left" valign="middle">1</td>
<td align="left" valign="middle">1</td>
</tr>
<tr>
<td align="left" valign="middle">struct, fixed</td>
<td align="left" valign="middle">1</td>
<td align="left" valign="middle">1</td>
</tr>
<tr>
<td align="left" valign="middle">struct, variable</td>
<td align="left" valign="middle">2</td>
<td align="left" valign="middle">2</td>
</tr>
<tr>
<td align="left" valign="middle">string</td>
<td align="left" valign="middle">2</td>
<td align="left" valign="middle">2</td>
</tr>
<tr>
<td align="left" valign="middle">wstring</td>
<td align="left" valign="middle">2</td>
<td align="left" valign="middle">2</td>
</tr>
<tr>
<td align="left" valign="middle">sequence</td>
<td align="left" valign="middle">2</td>
<td align="left" valign="middle">2</td>
</tr>
<tr>
<td align="left" valign="middle">array, fixed</td>
<td align="left" valign="middle">1</td>
<td align="left" valign="middle">3</td>
</tr>
<tr>
<td align="left" valign="middle">array, variable</td>
<td align="left" valign="middle">3</td>
<td align="left" valign="middle">3</td>
</tr>
</table>
<em>Table
6.4:
Client argument storage responsibility</em>
<table border="1" cellpadding="2" cellspacing="0">
<tr>
<td align="left" valign="middle">Case</td>
<td align="left" valign="middle">Description</td>
</tr>
<tr>
<td align="left" valign="middle">1</td>
<td align="left" valign="middle">Caller allocates all necessary storage, except that which may be encapsulated and managed within the parameter itself.</td>
</tr>
<tr>
<td align="left" valign="middle">2</td>
<td align="left" valign="middle">The caller allocates a pointer and passes it by reference to the callee. The callee sets the pointer to point to a valid instance of the parameter's type. The caller is responsible for releasing the returned storage. Following completion of a request, the caller is not allowed to modify any values in the returned storage. To do so the caller must first copy the returned instance into a new instance, then modify the new instance. </td>
</tr>
<tr>
<td align="left" valign="middle">3</td>
<td align="left" valign="middle">The caller allocates a pointer to an array slice which has all the same dimensions of the original array except the first, and passes it by reference to the callee. The callee sets the pointer to point to a valid instance of the array. The caller is responsible for releasing the returned storage. Following completion of a request, the caller is not allowed to modify any values in the returned storage. To do so the caller must first copy the returned instance into a new instance, then modify the new instance. </td>
</tr>
</table>
<em>Table
6.5:
Argument passing cases</em>
<p>The returned storage in case 2 and 3 is allocated as one block of memory
so it is possible to deallocate it with one call of CORBA_free.</p>
<h3><a name="id73513">6.10
Supported Memory Allocation Functions</a></h3>
<ul>
<li>
<p><strong>CORBA_Environment</strong> can be allocated from the user by calling
<strong>CORBA_Environment_alloc()</strong>.</p>
<p>The interface for this function is </p>
<p><span class="code">CORBA_Environment *CORBA_Environment_alloc(int inbufsz, int outbufsz);</span></p>
<p>where :</p>
<ul>
<li>
<p><strong>inbufsz</strong> is the desired size of input buffer</p>
</li>
<li>
<p><strong>outbufsz</strong> is the desired size of output buffer</p>
</li>
<li>
<p>return value is a <strong>pointer</strong> to an allocated and initialized
<strong>CORBA_Environment</strong> structure</p>
<p></p>
</li>
</ul>
</li>
<li>
<p>Strings can be allocated from the user by calling <strong>CORBA_string_alloc()</strong>.</p>
<p>The interface for this function is </p>
<p><span class="code">CORBA_char *CORBA_string_alloc(CORBA_unsigned_long len);</span></p>
<p>where :</p>
<ul>
<li>
<p><strong>len</strong> is the length of the string to be allocated.</p>
</li>
</ul>
</li>
</ul>
<p>Thus far, no other type allocation function is supported.</p>
<h3><a name="id73642">6.11
Special Memory Deallocation Functions</a></h3>
<ul>
<li>
<p><span class="code">void CORBA_free(void *storage)</span></p>
<p>This function will free storage allocated by the stub.</p>
</li>
<li>
<p><span class="code">void CORBA_exception_free(CORBA_environment *ev)</span></p>
<p>This function will free storage allocated under exception propagation. </p>
</li>
</ul>
<h3><a name="id73681">6.12
Exception Access Functions</a></h3>
<ul>
<li>
<p><span class="code">CORBA_char *CORBA_exception_id(CORBA_Environment *ev)</span></p>
<p>This function will return raised exception identity.</p>
</li>
<li>
<p><span class="code">void *CORBA_exception_value(CORBA_Environment *ev)</span></p>
<p>This function will return the value of a raised exception. </p>
</li>
</ul>
<h3><a name="id73720">6.13
Special Types</a></h3>
<ul>
<li>
<p>The erlang binary type has some special features.</p>
<p></p>
<p>While the <span class="code">erlang::binary</span> idl type has the same C-definition as
a generated sequence of octets :</p>
<div class="example"><pre>
module erlang
{
....
// an erlang binary
typedef sequence<octet> binary;
};
</pre></div>
<p>it provides a way on sending trasparent data between C and Erlang.</p>
<p>The C-definition (ic.h) for an erlang binary is :</p>
<div class="example"><pre>
typedef struct {
CORBA_unsigned_long _maximum;
CORBA_unsigned_long _length;
CORBA_octet* _buffer;
} erlang_binary; /* ERLANG BINARY */
</pre></div>
<p>The differences (between <span class="code">erlang::binary</span> and <span class="code">sequence< octet ></span>) are :</p>
<ul>
<li>
<p>on the erlang side the user is sending/receiving typical
built in erlang binaries, using <span class="code">term_to_binary() / binary_to_term()</span>
to create / extract binary structures.</p>
</li>
<li>
<p>no encoding/decoding functions are generated</p>
</li>
<li>
<p>the underlying protocol is more efficient than usual sequences of
octets</p>
</li>
</ul>
<p>The erlang binary IDL type is defined in <span class="code">erlang.idl</span>, while its
C definition is located in the <span class="code">ic.h</span> header file, both in the
<span class="code">IC-< vsn >/include</span> directory.
The user will have to include the file <span class="code">erlang.idl</span> in order to use the
<span class="code">erlang::binary</span> type.</p>
</li>
</ul>
<h3><a name="id73844">6.14
A Mapping Example</a></h3>
<p> <a name="stack_idl"></a>
This is a small example of a simple stack. There are two
operations on the stack, push and pop. The example shows all
generated files as well as conceptual usage of the stack.</p>
<div class="example"><pre>
// The source IDL file: stack.idl
struct s {
long l;
string s;
};
interface stack {
void push(in s val);
s pop();
};
</pre></div>
<p>When this file is compiled it produces four files, two for the
top scope and two for the stack interface scope. The important parts
of the generated C code for the stack API is shown below. <a name="stack_serv"></a>
</p>
<p>stack.c</p>
<div class="example"><pre>
void push(stack oe_obj, s val, CORBA_Environment* oe_env) {
...
}
s* pop(stack oe_obj, CORBA_Environment* oe_env) {
...
}
</pre></div>
<p>oe_stack.h</p>
<div class="example"><pre>
#ifndef OE_STACK_H
#define OE_STACK_H
/*------------------------------------------------------------
* Struct definition: s
*/
typedef struct {
long l;
char *s;
} s;
#endif
</pre></div>
<p>stack.h just contains an include statement of <span class="code">oe_stack.h</span>.</p>
<p>oe_code_s.c</p>
<div class="example"><pre>
int oe_sizecalc_s(CORBA_Environment
*oe_env, int* oe_size_count_index, int* oe_size) {
...
}
int oe_encode_s(CORBA_Environment *oe_env, s* oe_rec) {
...
}
int oe_decode_s(CORBA_Environment *oe_env, char *oe_first,
int* oe_outindex, s *oe_out) {
...
}
</pre></div>
<p>The only files that are really important are the <span class="code">.h</span>
files and the stack.c file.</p>
</div>
<div class="footer">
<hr>
<p>Copyright © 1998-2012 Ericsson AB. All Rights Reserved.</p>
</div>
</div>
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